Diesel engines are used in a wide variety of industrial applications. Common rail fuel systems are often used to deliver fuel to the engines and are generally known in the art of compression engines. Such systems use a fuel, such as distillate diesel fuel or heavy fuel oil, which ignites when placed under compression in a combustion chamber of the engine. A typical common rail fuel system includes a common fuel rail that supplies fuel injectors for an engine via quill tubes. Because of the high pressures involved, some jurisdictions require a double wall containment strategy for capturing leaked fuel. For instance, co-owned U.S. Patent Application Publication No. 2005/0166899 to Shamine et al. discloses a high pressure line connection strategy for fluidly connecting a common rail to fuel injectors.
Many industrial applications where compression engines are used would benefit environmentally and economically from use of gaseous fuels, such as natural gas, as the engine fuel. Natural gas is generally readily available and tends to be more economical. Additionally, combustion of gaseous fuels may reduce the production of undesirable emissions, including NOx, unburned hydrocarbons, and the like, thereby relaxing demands on aftertreatment systems. Furthermore, engines burning gaseous fuel generally have fewer maintenance problems.
While the use of gaseous fuel may provide the above advantages, gaseous fuel typically requires a much higher temperature to reach auto ignition than diesel fuel. Accordingly, some gaseous fuel engines include a spark plug. Other engines may use a small amount of distillate diesel fuel as a pilot fuel that is compression ignited to in turn ignite a larger charge of gaseous fuel, which is the primary fuel. Fuel systems that use both a compression fuel and a gaseous fuel are known as “dual fuel” systems.
Dual fuel systems typically require separate fuel paths into the combustion chamber of the engine. Canadian Patent 2,635,410, for example, teaches a dual fuel connector that relies upon a single quill that includes two different internal passages to facilitate fluid connection to two different fuel inlets of a fuel injector. This type of dual fuel connector has drawbacks because, at a minimum, the reference fails to teach an effective strategy for inhibiting fuel leakage. Alternatively, a coaxial quill assembly may be used to deliver the two fuels to the fuel injector, in which a first fuel path is defined by an inner quill and a second fuel path is defined by an annular space formed between the inner quill and an outer quill.
One challenge with the use of coaxial quill assemblies is to prevent leaks in the two fuel paths. An axial sealing load may be applied to each quill, thereby to seal the ends of the quill with abutting components. Because of the relative quantities, pressures, and properties of the primary fuel and the pilot fuel, the sealing load required for each quill may be different. Additionally, the engine may have different modes of operation that change the desired operating pressures of the fuels, and therefore the required sealing load for a given quill may change depending on the engine mode of operation. Accordingly, it is desirable to provide a quill assembly that adequately seals the quills while addressing the different fuel pressures and modes of operation in a duel fuel engine.